GT Motorsports: 370Z Supercharger system development

KEVTEX

With a turbo, the engine has to work harder to get the exhaust out because of the increased back pressure the turbo provides. The same amount of extra work is required if you take the power from a crank pulley.

RCZ

Not at all because the sc has to move gearing and a belt while the tc only has to spin. We aren't arguing for the sake of argument, we know this is and has always been the case. In modern days, parasitic losses from the sc have been greatly reduced through new designs, but its still takes a bigger toll on the engine to make the power.


Also, guys, the whole bigger turbo makes more power thing.... From what I understand its not because it flows more, we know that 5psi is 5psi. What matters is the charge density of that 5psi. According to what Silo posted, a turbo that is in its peak efficiency zone (or island if you've ever seen a turbo flow chart) will create a more dense 5psi than one that is not. Think of it this way... colder air is denser, air particles are more compact therefore there is more oxygen to burn therefore you make more power. The same apparently goes for a turbo operating at peak efficiency vs one that isnt. The one operating at peak eff. somehow produces a more dense charge (at the same temperature) as the one that is out of its efficiency zone.

The post by silo didnt explain why, but I have a feeling it has something to do with how the air is compressed in a more efficiently sized tc than a less efficiently sized one. Efficiency relating to the size of the engine and the amount of psi you are targeting.

I'll do some more research and let you guys know.

Silo

That was my point. A larger turbo, and i have to state more specific, at a given psi might be more efficient, which means will it heat the charge less, hence more oxygen in that charge.

One simple factor is that it has to "shovel" less. You have a larger shovel you will dig that whole more efficiently than with a spoon. The other factor might be that the exhaust side is larger and therefore pumping loss is reduced. The larger turbo might still be less efficient at a lower psi but usually we compare the peak operating psi range.

kdoske

I see what kevtex is saying. Laws of physics will tell you the same amount of energy is used to create say 6lbs of boost whether it be by pulley or exhaust. I totally agree with that, but the energy used by the exhaust while exactly the same as the energy used by the pulley does create different effects on the engines HP/TQ output. I still say using the exhaust pressure is more efficient for the engine to create boost and not have such and adverse effect on the current HP output, but yes, it does exhaust the same amount of energy on an atomic level as with the pulley.